M.O.R.E. Journal - Medacta M.O.R.E...medacta® orthopaedic research and education Institute,...

3 Cementless HA coated Quadra® stem - 7 years clinical outcomes

7 NJRR Report 2011, Quadra® stem Results

11 Experimental assessment of the cemented AMIStem-C implant stability

17 Impact of cup design in reducing the risk of dislocation

22 Preoperative planning accuracy of MyKnee® system

26 Cadaver test and MRI kinematic study of the flat lateral and congruent lateral tibial inserts of the GMK® Sphere implant

32 Mechanical Stability of the AMIStem, a Standardized In-Vitro Analysis

M.O.R.E. JournalV O L U M E 0 2

JANUARY 2012

The official Journal of the

m.o

.r.e Journal - January 2012, Volum

e 02

medacta® orthopaedic research and education Institute, m.o.r.e. Institute, has been created to provide continuous support for healthcare professionals in the field of research and education.

The m.o.r.e. Institute offers Surgeon to Surgeon educational opportunities to share experience and improve patient outcome.

M E D A C T A O R T H O P A E D I CR E S E A R C H A N D ED U C AT I O N

I n s t I t u t e

.O.R.E.I n s t I t u t e

m.o.r.e. Journal - January 2012, Volume 02

a. Polyclinique Montier la Celle, St André les Vergers controlateral THA) (B2) - Franceb. Medacta® International, Research & Development department, Castel San Pietro, CHc. Medacta® International, Medical department, Castel San Pietro, CHd. Medacta® International, Product Management department, Castel San Pietro, CHe. Aurora Memorial Hospital, Burlington - USAf. North Austin Medical Center, Austin - USAg. Peak Orthopaedics and Spine, Colorado - USAh. Pampa regional medical center, Texas - USAi. Dixie Regional Medical Center, Utah - USAj. UHS- Kenosha, Wisconsis - USAk. First Orthopaedic Clinic, Charles University, Prague, Czech Republic l. Institute of Orthopaedics and Musculoskeletal, University, College, 79 Albert Street, NW1 7LX London, UKm. School of Engineering Sciences, Southampton University, Southampton, UKn. The Royal London Hospital, London, UK

m. Bernardonib, F. Siccardic, I. Quaglianad, G. Grimoldid

Mechanical Stability of the AMIStem, a Standardized In-Vitro Analysis



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Cementless HA coated Quadra® stem - 7 years clinical outcomes

Abstract The purpose of this clinical study is to assess prospectively, in a homogeneous series of patients, the clinical and radiological outcome of a cementless HA coated Quadra® prosthesis at seven years follow-up. The series include 97 stems implanted between January 2003 and January 2005 by the same surgeon. 5 (5.6%) patients died and 8 (9%)were lost to follow-up. The Harris Hip Score mean value is 98.4 (±6.1). The only two revisions were due to an infection and a fracture in the metaphyseal femoral zone after surgery. According to the Kaplan meyer method, 7 years survival rate is 100% considering aseptic loosening and 97% considering any reason as endpoint.

Cementless HA coated Quadra® stem7 YeArS CLINICAL oUTComeS

P. moreaua

IntroductionThe aim of the current clinical study is to evaluate the

performance and the security of cementless HA coated Quadra® stem (Quadra®-H, medacta® International SA, Switzerland).

each implant has been the object of a pre-operative clinical and radiological examination as well as a post-operative one at different periods of time.

The parameters taken into consideration, to record the clinical/functional outcome, are both subjective and physical: such as the Harris Hip Score (HHS) and the range of motion. From the radiological point of view, particular attention has been paid to the position of the implant and the presence of radiolucency. The area around the stem has been divided into 7 different zones as described by Gruen et al.[1,2] (Figure 1).

only radiolucencies bigger than 2 mm have been considered as critical as this is considered by many authors to be a sign of probable aseptic loosening in the future[2, 3].

Figure 1. Areas with possible radiolucency around the stem. a. Polyclinique Montier la Celle, St André les Vergers controlateral THA) (B2) - France

The survival rate of the stem has been computed considering any reason with the aseptic loosening as endpoint.

All the data allows the evaluation of the patient’s ability and capacity to use the prosthetic joint in normal daily activities.

material and methodBetween January 2003 and January 2005, 89 patients

(with a total of 97 procedures) underwent a primary total hip arthroplasty using a cementless, Quadra®-H stem coupled with press fit cups provided by different suppliers. All operations were performed by the same surgeon (Dr. Pascal moreau) in the same hospital (Polyclinique montier la Celle, St André les Vergers – France).

of the 89 patients, 52 were men and 37 were women.Their mean age at the date of surgery was 66 years (34 to 83) and the mean BmI (kg/m2) was 27.7 (16.6 to 40.6). None of the 8 bilateral operations were performed simultaneously.

The main diagnosis was osteoarthritis for most of the patients (83.5%), followed by osteonecrosis (11.4%), dysplasia (4.1%) and inflammatory arthritis (1%).

Among these cases, 7 patients had a previous surgery: 4 were osteosynthesis after a femoral neck fracture, 2 roof plasty and 1 femoral osteotomy.

m.o.r.e. Journal 2012; 2: 3-6 ref. 99.99.JoUrNAL02-3 rev.00

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The patients were divided into three categories (A, B and C) on the basis of Charnley classification in order to gain better understanding of the variability in outcome:

• 47.4% were unilaterally joint diseased (A)• 30.9% were bilaterally joint diseased (B1)• 20.6% were bilaterally joint diseased (with

controlateral THA) (B2) • 2.1% reported conditions directly impairing the

act of walking, with limited function even if joints were normal (C)

The preoperative clinical evaluation showed a mean HHS of 39 points (±9.6). All the surgeries were conventional total hip arthroplasty performed through the surgical approach Posterior moore. A trochanter osteotomy was never done; acetabular and femoral bone grafts were never used.

The patients were followed up with controlled visits at different time points: 3 months, 1, 3 and 7 years after surgery.

Statistical analysisDescriptive analysis was performed with the use of

univariate statistics for the continuous variables and frequency distribution for the categorical variables. results are reported as means and standard deviations.

The survival rate was calculated on the basis of Kaplan meyer method. In order to evaluate the difference between the preoperative and postoperative group, paired Student’s t-tests were performed. The results of these comparisons are reported as p-value (<0.05).

results and discussionFrom the last follow-up, we report the results for

76 patients: 31 performed a clinical and radiological visit, 7 remained available for radiographic follow-up and 3 for clinical follow-up. 35 patients refused to perform a control visit and were contacted by a phone call in order to assess the status of their prosthesis. Additionally 8 patients were lost to follow-up as they were not traceable.

During the study period, 5 patients died of unrelated causes to the prosthetic system (2 at 1 year, 1 at 3 years and 2 at 7 years after surgery) and 2 patients underwent revision surgery. one patient was revised, 7 days after the first surgery because of a fracture in the metaphyseal femoral zone, due to reason not related to the implants, and the other one because of infection at 7 years postsurgery.

The prosthetic systems were radiographically evaluated in order to assess the stem and cup position after surgery. The stem resulted in neutral position in the 97.9% of cases and the cup has an inclination of 41-45° (86.6%) and an anteversion of 10-15°(96.9%).

98% of the patients had no intraoperative complications, in 2 cases an intra-operative femoral fracture (1 distal, 1 proximal) occurred. A wiring procedure was performed and there were no further complications.

Postoperatively, one patient reported a urological complication and two patients had a hematoma. There were also minor complications summarized below:

• a reduced posterior dislocation, occurred 15 days after surgery;

• a calcar fracture, occurred 1 month after surgery, which led to stem subsidence of 10 mm;

All these complication were resolved without clinical critical consequences.

Following surgery, the Harris Hip Score significantly increased above 60 points at 3 months maintaining this result with time (Figure 2).

At 7 years the mean HHS is 98.4 (±6.1); it decreased slightly, without significant differences in comparison to 3 years follow-up data (99.4±3.3). This could be due to the occurrence of concomitant pathologies mobility invalidating, for example, low back pain, controlateral coxarthrosis, hip fracture.

However 100% of patients did not report further hip pain.

Figure 2. Graphical representation of time trend of HHS.

Time

HH

S

presurgery

5




In most of the cases, the functionality gained has been maintained:

• 96.5% of patients can reach a distance > 1000 m, while before surgery, only 10% could achieve this.

• 93.1% of patients can walk without any support; only one patient still uses a cane for long walks and one patient a crutch.

• 96.5% of patients can walk up and down stairs normally without limping; 82.8% have no difficulties putting on shoes/socks.

• All patients are able to sit comfortably in any chair.

overall a great improvement in mobility was reported at the first controlled visit. At 3 years after surgery, 50% of the patients recorded the rom for both, the operated and the controlateral leg, and it has to be noted that the values recorded are similar, underlining the full functional recovery of movement (132.05±15.86 and 132.05±18.23 for operated leg and controlateral leg respectively).

Figure 3 shows the mean range of motion values measured at all time points: before surgery, at 3 months, 1, 3 and 7 years after intervention.

Figure 3. Graphical representation of time trend of rom.

From a radiological point of view, no problem of loosening of the femoral or the acetabular component occurred. All components seem stable and well fixed, as shown in Figure 4, which reports the clinical case of a 73 year old patient at 7 years follow-up control. There was no occurrence of bone penetration, implant breakage or stem subsidence.

At the last follow-up, 2 patients showed radiolucencies bigger than 2 mm in Gruen zone 3 and 6. reported so far, no complications have been reported and the patients will continue to be monitored in time.

Figure 4. X-ray image of 73 years old woman, 7 years postoperative.

The survival rate of the stem at 7 years after surgery is 100% considering aseptic loosening and 97% considering any reason as endpoint. In Figure 5 shows the survival curves of the prosthesis considering any reason as endpoint.

Figure 5. Kaplan meyer survival curve considering any reason as endpoint.

Time

presurgery

ROM

[ ]

Time (months)

Cum

ulat

ive

prop

ortio

n su

rviv

ing

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ConclusionThese are promising results at mid term for an initial

series of subjects, with a Quadra®-H stem as part of their THA. The 7 year survival rate of the stem is 100% considering aseptic loosening and 97% considering any reason as endpoint. These satisfactory results are in line with data reported in literature for the Zweymuller and Corail stems, the concepts of which were used to develop the Quadra® stem design[4,5,6].

references[1] Johnston rC, Fitzgerald rH Jr, Harris WH, Poss r, müller me, Sledge CB, “Clinical and radiographic evaluation of total hip replacement. A standard system of terminology for reporting results”. J Bone Joint Surg Am. 1990; 72:161-168.

[2] engh CA, Bobyn JD, Glassman AH, “Porous-coated hip replacement. The factors governing bone ingrowth, stress shielding, and clinical results”. J Bone Joint Surg Am 1988; 69:45-55.

[3] Narasimha Am, Scott G, Freeman mAr, “Hydroxyapatite-Coated femoral components in total knee arthroplasty”. J. Arthroplasty 2003; 18: 844-851.

[4] Suckel A, Geiger F, Kinzl F, Wulker N, Garbrecht m, “Long-term results for the uncemented Zweymuller/Alloclassic hip endoprosthesis”. J. Arthroplasty 2009; 24 (6): 846-53.

[5] reigstad o, Siewers P, røkkum m, espehaug B, “Excellent long-term survival of uncemented press-fit stem and screw cup in young patients”. Acta orthopaedica 2008;79(2):194-202.

[6] Hallan G, Lie SA, Furnes o, engesaeter LB, Vollset Se, Havelin LI, “Medium- and long-term performance of 11516 uncemented primary femoral stems from the Norwegian arthroplasty register”. J Bone Joint Surg Br. 2007;89-B:1574-80.

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NJrr report 2011, Quadra® stem results

NJrr report 2011, Quadra® stem resultsm. Bernardonia, F. Siccardib, I. Quaglianac, S. Camesascac

IntroductionThe Australian National Joint replacement registry

(NJrr[1-3]) collects data on joint replacement surgeries in Australia. The Australian orthopaedic Association (AoA) recognised the need to establish a National Joint replacement registry in 1993. At that time, the outcome of joint replacement in Australian was unknown; it was not apparent who was receiving joint replacement or the types of prostheses and techniques used to implant them. The need to establish a registry was in part based on the documented success of a number of arthroplasty registers in other countries, in particular the Swedish arthroplasty registries.

The Australian registry began data collection on 1 September 1999 and its purpose is to define, improve and maintain the quality of care provided to individuals receiving joint replacement surgery.

Abstract The Australian National Joint replacement registry (NJrr) collects data on joint replacement surgeries in Australia. The 2011 register report, relative to 2010 data, confirms positive data on the Quadra®-H stem (medacta® International SA), showing that: • Quadra®-H is the 3rd most implanted cementless stem in Australia for 2010 (with almost 1000 stems implanted in 2010), only 3 years after its introduction in the Australian market. It is the 5th most implanted stem when cemented stems are included.• Almost 95% of Quadra®-H are implanted using the AmIS® technique by surgeons new to the direct anterior approach. • Many revisions are related to other components, not to Quadra®-H. • There is no difference in the risk of revision with Quadra®-H when compared to all other THr after the first two weeks of implantation. • In the first two weeks only, the risk of revision is over 2.5 times the risk of revision of all other THR. This demonstrates that Quadra®-H revisions are not related to the implant, but clearly related to the learning curve for new users of the anterior minimally invasive surgery (AmIS®, medacta® International SA). • There were 1808 primary procedures registered by the NJRR at the end of 2010. The Quadra®-H revision rate is decreasing year by year and on current indications, can reasonably be expected to be lower than the national threshold of the critical revision rate in 2011.

material and methodsThe purpose of this study was to analyse the

performance of the Quadra®-H stem considering the revision rate and the revision risk results reported in the Australian National Joint replacement registry.

The revision rate for each prosthesis is compared with the national threshold of critical revision rate, i.e. double the revision rate value registered for all total conventional hip prostheses. In the NJrr 2011[1] (relative to 2010 data) this threshold is set at 1.56.

The revision rate is calculated dividing the total revision number by the “observed components years” for a specific prosthesis.

As explained in the Australian report, for each procedure, its component time (“observed components years”) is the time during which it is at risk of being revised. This is calculated as the number of days from the date of the primary procedure until either the date of revision, date of death or end of study whichever occurs first. This is then divided by 365.25 to obtain the number of “observed component years”.


a. Medacta® International, Research & Development department, Castel San Pietro, Switzerlandb. Medacta® International, Medical department, Castel San Pietro, Switzerlandc. Medacta® International, Product Management department, Castel San Pietro, Switzerland

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each primary procedure then contributes this calculated number of component years to the overall total component years for a particular category of prosthesis.

The risk of revision (or “hazard ratio”) is instead an estimate of the instantaneous risk of revision, at a point in time, t.

This study reports the NJrr estimate of Quadra®-H risk of revision compared with other conventional total hip replacement stems risk of revision.

results and discussionThe 2011 register report for 2010 THr procedures

(page 42 NJrr[1]) provides positive data on the Quadra®-H stem. It shows that Quadra®-H is the 3rd most implanted cementless stem in Australia for 2010 (with almost 1000 stems implanted in 2010), only 3 years after its introduction in the Australian market. It is the 5th most implanted stem when cemented stems are included.

There were 1808 procedures registered by the NJrr at the end of 2010 and the Quadra®-H revision rate (shown in the graph below) is decreasing year by year, and can reasonably be expected to be lower than the national threshold of the critical revision rate in 2011.

2010200920082007

1200

1000

800

600

400

200

0

1.85

3.3

6.7

1.56

National threshold of Critical revision rate

QUADRA®

Revisions/100 obs year

N˚ Surgeries

Figure 1. Number of Quadra® Surgeries & NJrr revision rate.

When observing this graph of the Quadra®-H Stem (Figure 1), it must be taken into account that the stem was only introduced in Australia in late 2007 together with the Anterior minimally Invasive Surgery (AmIS®, medacta International SA).

The AmIS® approach is a proven technique that has been used worldwide since 2004 with more than 60,000 procedures performed up to october 2011. on a global scale more than 80% of Quadra®-H stems are implanted using this technique (in Australia almost 95%).

There are many benefits for patients, however, surgeons require a period of learning (learning curve).

As shown in the graph, in the past (years 2008, 2009 and 2010) the Quadra®-H revision rate was higher than the critical national threshold. These complications however were mainly related to the fact that Quadra®-H implantations were carried out by many different surgeons in the early stages of their AmIS® learning curve. Furthermore the ratio of complications reported in Australia should not be considered alarming in relation to AmIS®; it is at the same level as those published for other learning curves[4-13].

It is also confirmed that the Quadra®-H revision

rate is progressively decreasing, while the number of surgeries is increasing year by year. Surgeons are gaining experience and therefore reducing the Quadra®-H revision rate. The fact that the rate of revision has dramatically decreased, is testimony to the effectiveness of AmIS® educational programme.

It must also be noted that there is no difference in the risk of revision between Quadra®-H and all other THr after the first two weeks. As reported in the AoA NJrr Annual report 2011 (page 164 NJrr[1]), the risk of revision for the Quadra®-H femoral component was over 2.5 times the risk of revision in the first two weeks only compared to all other THr, but there is no difference in the risk of revision after two weeks.

As shown in the graphs below (Figures 2 and 3), it is worth noting that the risk of revision (Hazard ratio, page 193 NJrr[1]) for the Quadra®-H in the first two weeks compared to all other THr, is almost halved in 2010 (2.77 in 2010 vs 5.12 in 2009) and compared to all other THr, there is no difference after two weeks.

Hazard Ratio 0-2 wk11.3

5.12

2.77

2008 2009 2010

12

10

8

6

4

2

0

Figure 2. Quadra® stem Hazard ratio 0-2 weeks.

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Cum

ulat

ive

Perc

ent R

evis

ion

Years Since Primary Procedure

HR - adjusted for age and gender

Quadra®-H vs Other Total Conventional Hip 0 - 2Wk HR=2.77 (1.60, 4.81),p<0.001 2Wk+ HR=0.98 (0.65, 1.47),p=0.911

Quadra®-HOther Total Conventional Hip

0%

5%

10%

15%

20%

25%

30%

0 1 2 3 4 5 6 7 8 9 10

Figure 3. Quadra®-H vs other Total Conventional Hip cumulative percent revision.

As most of these revisions were performed within a few days post-surgery, they can be considered as approach-related and not implant-related. In fact there is a high probability of detecting surgical error during the surgery or a few days post-op, due to the surgeon’s learning curve.

This data demonstrates how effective and important the AmIS® education programme has been in Australia: while the number of surgeries continues to increase and the surgeons gain more experience, the Quadra®-H revision rate decreases year by year.

It is important to emphasise that, of the 36 revisions reported in the AoA NJrr Annual report 2011:

• 19 are surely not Quadra®-H stem related but related to other factors;

• 14 involve the Quadra®-H stem as listed: 5 are traumatic fractures; 6 are infections; 3 are intra-operative fractures;

• 3 could not be clearly categorised.

According to this data, Quadra®-H results are promising. This is also demonstrated in Dr. Dora’s publication at 5 years of follow up[14] and Dr. moreau’s report at 7 years of follow up[15].

Conclusion

The 2011 register report confirms positive data on the Quadra®-H stem, showing that there were 1808 procedures registered by the NJrr at the end of 2010. The Quadra®-H revision rate is decreasing year by year and by current indications can reasonably be expected to be lower than the national threshold of the critical revision rate in 2011.

many revisions are related to other components and not to Quadra®-H and it is important to consider that:

• There is no difference in the risk of revision after the first weeks between Quadra®-H and all other THr.

• Only in the first two weeks the risk of revision is over 2.5 times the risk of revision of all other THr.

This demonstrates that Quadra®-H revisions are not related to the implant, but clearly related to the learning curve for new users of AmIS®. These excellent results confirm:

• The good performance of the Quadra®-H stem, which is the 3rd most implanted cementless stem in Australia for 2010 (with almost 1000 stems implanted in 2010), only 3 years after its introduction in the Australian market;

• Medacta’s commitment to education when introducing a new surgical technique for the benefit of the orthopaedic community.

references[1] AoANJrr “Annual Report 2011”.

[2] AoANJrr “Annual Report 2010”.

[3] AoANJrr “Annual Report 2009”.

[4] Woolson ST, mow CS, Syquia JF, Lannin JV, Schurman DJ, “1. Comparison of primary total hip replacements performed with a standard Incision or a mini-Incision”. JBJS 2004; 86-A(7):1353-8.

[5] Levine Br, Klein Gr, Di Cesare Pe, “2. Surgical approaches in total hip arthroplasty”. Bulletin of the NYU Hospital for Joint Diseases 2007;65(1):5-18.[6] Seng Be, Berend Kr, Ajluni AF, Lombardi AV Jr, “Anterior-supine minimally invasive hip arthroplasty: defining the learning curve”. orthop Clin N Am 2009;40:343-350.

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[7] D’Arrigo C, Speranza A, monaco e, Carcangiu A, Ferretti A, “Learning curve in tissue sparing total hip replacement: comparison between different approaches”. J orthopaed Traumatol 2009;10:47-54.

[8] Bal BS, Haltom D, Aleto T, Barrett m, “Early complications of primary total hip replacement performed with a two-incision minimally invasive technique”. JBJS 2005;87-A(11):2432-8.

[9] Laffosse Jm, Chiron P, molinier F, Bensafi H, Puget J, “Prospective and comparative study of the anterolateral mini-invasive approach versus minimally invasive posterior approach for primary total hip replacement. Early results”. International orthopaedics 2007;31:597-603.

[10] mears DC, “Development of a two-incision minimally invasive total hip replacement”. JBJS 2003;85-A(11):2238-40.

[11] Swanson TV, “Posterior single-incision approach to minimally invasive total hip arthroplasty”. International orthopaedics 2007;31(Suppl 1):S1-S5.

[12] Wohlrab D, Sotereanos N, “9. Experience with the two incision minimal invasive hip replacement in 150 cases with a proximally hydroxyapatite coated implant”. Acta orthop Traumatolog Cech 2009;76(4):276-80.

[13] Goosen JH, Kollen BJ, Castelein rm, Kuipers Bm, Verheyen CC, “Minimally invasive versus classic procedures in total hip arthroplasty”. Clin orthop relat res – Published online: 30 march 2010.

[14] müller DA, Zingg P, Dora C, “5 year survival and radiological outcome of minimally invasive total hip replacements using a relatively new implant (Quadra®/Versafitcup®, Medacta®, Switzerland)”. SGo 2011, 22th-24th June, Lausanne.

[15] moreau P, “Study Report – Cementless HA coated Quadra® stem 7 years clinical outcomes”. 2011, White Paper.

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experimental assessment of the cemented AmIStem-C implant stability

experimental assessment of the cemented AmIStem-C implant stability m. Bernardonia, F. Siccardib, I. Quaglianac, S. Camesascac

IntroductionThe AmIStem-C (medacta® International SA) is the

first cemented femoral stem specifically designed for anterior minimally invasive surgery. It is made of high nitrogen stainless steel, with a mirror polished surface which should not cause any cracks or gaps in the cement mantle.

The AmIStem-C has been designed to offer more bone preservation and easier introduction into the femoral canal preserving effective mechanical stability.

Abstract The AmIStem-C (medacta® International SA) is the first cemented femoral stem specifically designed for anterior minimally invasive surgery. It is made of high nitrogen stainless steel, with a mirror polished surface which should not cause any cracks or gaps in the cement mantle. The AmIStem-C has been designed to offer more bone preservation and easier introduction into the femoral canal preserving effective mechanical stability. Aim of this study is to assess the AmIStem-C dynamic stability, comparing AmIStem-C mechanical tests results with well performing cemented implants. For this purpose, reconstructions in synthetic femurs (n=5) were realized both for AmIStem-C and Cone* implants (medacta® International SA), which were adopted as a reference. The reconstructions were subjected to 250,000 cycles of normal walking. Subsequently, they were subjected to 75,000 cycles of dynamic torsional load. During the experiments the migration of the implants with respect to the bone was measured using rSA. For both implant designs, the two reconstructions with the largest migration values were sectioned and compared with unloaded reconstructions. In general, AmIStem-C migration and rotation were minimal and within the range of clinically well-functioning implants that have been tested in a similar manner. In sectioned specimens of reconstructions with both implant designs, no cement cracks, implant-cement gaps or large pores were found, nor were there noteworthy differences found between the tested reconstructions and the unloaded specimens. According to these results, we conclude that the AmIStem-C femoral stem provides good initial stability and that its migration patterns are comparable to those of clinically well-performing implants. Furthermore, the absence of cement cracks and gaps demonstrates the AmIStem-C provides an adequate load transfer from implant to cement mantle to periprosthetic bone.

*The Cone prosthesis is not FDA clearedm.o.r.e. Journal 2012; 2: 11-16 ref. 99.99.JoUrNAL02-11 rev.00

Figure 1. The AmIStem-C femoral stem (left) and the Cone* prosthesis (right).

a. Medacta® International, Research & Development department, Castel San Pietro, Switzerlandb. Medacta® International, Medical department, Castel San Pietro, Switzerlandc. Medacta® International, Product Management department, Castel San Pietro, Switzerland

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bone cement (Heraeus Kulzer GmbH, Germany), using third generation cementing techniques, including the use of a cement plug, vacuum mixing of the cement (Palamix - Heraeus medical GmbH, Germany), and cement pressurization.

The AmIStem-C implants were inserted without centralizers, while the Cone* stems were inserted using a proximal and distal centralizer.

In total, six reconstructions were prepared with each implant design, of which five were loaded in experiments while one served as an unloaded control.

The reconstructions were subjected to a dynamic loading regime (frequency 1.0 Hz) simulating the stance phase of normal walking. The hip joint contact load was applied to the prosthetic head, with an amplitude of 2.44 times body weight (1700 N; [3]). The stance phase load was applied for a total of 250,000 cycles for each specimen. Subsequently, the specimens were exposed to a dynamic torque load (frequency 1.0 Hz) to measure the rotational stability of the reconstructions. The magnitude of the torque load was roughly two times the maximal stair climbing load (37.5 Nm; Heller et al., 2001) and was applied for 75,000 cycles. All experiments were performed under simulated physiological conditions (saline, 37°C; Figure 3).

A. Bag to drain water basin during rSA measurements.B. Fixture for application of the torque load.C. Water basin with a reconstruction in situ. D. Water circulation pump and heating. e. X-ray source of the rSA set-up.

Figure 3. experimental set-up during the torque experiments. Indicated is also the coordinate system for the rSA measurements (x-axis = latero-medial; y-axis = distal-proximal; z-axis = posterior-anterior direction).

methods All tests have been performed at the orthopaedic

research Laboratory in the radboud University Nijmegen medical Centre (The Netherlands).

reconstructions with the AmIStem-C stem and the Cone* implants were created in composite femurs (type 3406, Sawbones, Vashon, WA). Both implant designs were pre-planned based on AP and mL radiographs of the composite femur (AmIStem-C reconstruction in shown in Figure 2). The templates of the Cone* stem already included the cement mantle; a size 7 proved to be the best fit. The template of the AmIStem-C only included the implant geometry. A size 6 was found to provide an adequate fill of the femoral canal. For the current study, rather than using a line-to-line technique (broach size equals stem size), we chose to provide a thick and complete cement mantle surrounding the implant. Hence, we implanted a size 5 AmIStem-C implant in a cavity reamed with a broach of size 6.

Figure 2. Pre-planning of the AmIStem-C in AP and mL radiographs of the composite femur.

All reconstructions were prepared by an experienced surgeon (JN). The stems were implanted in Palacos r


The current study describes the experimental assessment of the stability of reconstructions with the cemented AmIStem-C femoral stem (Figure 1), comparing mechanical tests results with the well-performing cemented Cone* implant[1,2], taken as a reference (both medacta® International SA, Switzerland).

The Cone* cemented implant is characterized by good stability, consistent circumferential cement mantle, adequate subsidence and rotation[1,2], therefore it was chosen as a reference. Furthermore, it was investigated whether migration is associated with gap formation at the stem-cement interface or failure within the cement.

*The Cone prosthesis is not FDA cleared

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During the experiments the 3-D migration (translation and rotation) of the stem relative to the bone was measured using roentgen Stereophotogrammetric Analysis (RSA; error 40 μm [4]). For this purpose tantalum markers were inserted in the bone and attached to the prosthesis.

During the stance phase loading regime, rSA measurements were performed at 0 - 1,000 - 10,000 - 50,000 - 100,000 - 200,000 - 250,000 cycles. During the torque load tests rSA measurements were performed at 0 - 1,000 - 10,000 - 25,000 - 75,000 cycles. All translations and rotations were calculated relative to the tip of the implant. Statistical significance of differences between the two groups at the end of the walking and stair climbing loading regime was tested using Student’s T-tests for all directions independently.

After the experiments, of each group (AmIStem-C and Cone*) the two reconstructions with the highest migration were sectioned using a diamond blade sawing machine. The sections were stained with black shoe polish, after which they were sanded and polished to remove surface stain. The sections were then inspected for stem-cement interface gaps, cement cracks and porosity patterns using digital images of the sections. The unloaded specimens were also sectioned and analyzed as a reference. For each reconstruction 5 equidistant sections were made, ranging from the calcar region to the implant tip level.

resultsWalking load experiments

None of the reconstructions failed or showed signs of gross loosening during the walking load experiments. At the end of the loading regime, the average rotations and translations remained relatively low (max. translation 0.410 mm vs. 0.166 and max. rotation 0.366° vs. 0.176°; AmIStem-C vs. Cone*, respectively (Figure 4)). The largest changes in implant rotation or translation generally occurred during the first 10,000 cycles.

∆

Figure 4a. Average rotations of the reconstructions with the AmIStem-C and Cone* implants during the walking load experiments.

∆ Statistical significant difference (p<0.001)

0.0E+005.0E+04

1.0E+051.5E+05

2.0E+052.5E+05

0.0E+005.0E+04

1.0E+051.5E+05

2.0E+052.5E+05

0.0E+005.0E+04

1.0E+051.5E+05

2.0E+052.5E+05


14



∆

Figure 4b. Average translations of the reconstructions with the AmIStem-C and Cone* implants during the walking load experiments.

∆ Statistical significant difference (p<0.001)



∆

Figure 5a. Average rotations of the reconstructions with the AmIStem-C and Cone* implants during the torque load experiments.

In all directions, no significant differences were found between the AmIStem-C and the Cone* reconstructions, except at the end of the walking loading regime, where the AmIStem-C implants displayed just a slight rotation around the z-axis (valgus) and a slight migration in the anterior direction. It is however important to underline that AmIStem-C migration and rotation were minimal and within the range of clinically well-functioning implants that have been tested in a similar manner.

0.0E+005.0E+04

1.0E+051.5E+05

2.0E+052.5E+05

0.0E+005.0E+04

1.0E+051.5E+05

2.0E+052.5E+05

0.0E+005.0E+04

1.0E+051.5E+05

2.0E+052.5E+05

0.0E+002.5E+04

5.0E+047.5E+04

0.0E+002.5E+04

5.0E+047.5E+04

0.0E+002.5E+04

5.0E+047.5E+04

15



As expected, the largest rotations were found in retroversion, resulting from the torque component of the stair-climbing load. In all directions, no significant differences were found between the AmIStem-C and Cone* reconstructions.

Sections

of both implant design groups, the two poorest performing reconstructions were sectioned and analyzed for stem-cement interface gaps, cement cracks and porosity patterns. Five equidistant sections were created, from the level 5 mm below the calcar to the implant tip level (an example of Cone* reconstruction is shown in Figure 6).

Figure 6. example of a sectioned Cone* reconstruction.

Visual inspection of the tested AmIStem-C and Cone* sections did not reveal any cracks in the bulk cement, implant-cement interface or cement-bone interface (Figure 7).

In addition, virtually no gaps were observed at the implant-cement interface. Some micropores were found at the implant-cement interface, and a few larger pores in the bulk cement; the porosity distribution was similar for both implant designs. With both the AmIStem-C and Cone* implants, the tested reconstructions did not differ dramatically from the unloaded specimens. Sections and post-operative radiographs indicated AmIStem-C designs were aligned properly within the femoral canal.

In summary, no noteworthy phenomena were found in the sectioned reconstructions. We did not observe significant differences between the AmIStem-C and the Cone* reference, nor did the tested reconstructions differ dramatically from the untested specimens.



Figure 5b. Average translations of the reconstructions with the AmIStem-C and Cone* implants during the torque load experiments.

Stair climbing load experiments

Also during the stair climbing load experiments no gross failures were observed in both AmIStem-C implant and Cone* reference groups. Due to the nature of the loading regime, migrations were lower than during the walking regime, while the implant rotations were slightly higher (max. translation 0.184 mm vs. 0.116 mm and max. rotation 0.510° vs. 0.666°; AmIStem-C vs. Cone*, respectively (Figure 5)).

0.0E+002.5E+04

5.0E+047.5E+04

0.0E+002.5E+04

5.0E+047.5E+04

0.0E+002.5E+04

5.0E+047.5E+04

16



Figure 7. Sections of reconstructions with the AmIStem-C (left) and Cone* implants (right).

DiscussionThe objective of the current study was to measure the

axial and rotational stability of the cemented AmIStem-C. For this purpose the Cone* well-performing implant[1,2] was taken as a reference; furthermore it was investigated whether migration was associated with gap formation at the stem-cement interface or failure within the cement.

In general, we can confirm that AmIStem-C migration and rotation were minimal. reviewing the data retrieved from all specimens, the maximal translation measured was 0.781 mm and the maximal rotation was 0.890°. This indicates that the reconstructions with the AmIStem-C implants were very stable under the current loading regimes. moreover, the migration values are within the range of clinically well-functioning implants that have been tested in a similar manner, such as the Lubinus SPII[5,6]. The relatively low migration and rotation values found in the rSA results proves the absence of cement cracks, implant-cement gaps and large pores in the cement mantle in the sectioned specimens. No noteworthy differences were found between the AmIStem-C and the Cone* reference sections, nor did the tested reconstructions differ from the unloaded specimens that were sectioned as a control. These observations indicate that the external loads were well transferred to the composite femur by the cement mantle.



Conclusion

mechanical tests performed in this study demonstrate the AmIStem-C femoral stem provides a good initial stability, in particular:

• the migration patterns of the AMIStem-C are comparable to those of Cone* (here taken as a reference) and clinically well-performing implants that have been tested in similar experiments;

• the absence of cement cracks and gaps demonstrate the AmIStem-C femoral implant provides an adequate load transfer from implant to cement antle to periprosthetic bone.

In conclusion, we can confirm that the AmIStem-C femoral stem is a reliable cemented implant.

references[1] J. de Waal malefijt, J. Nieuwenhuis, T. Gosens, “The cone cemented hip arthroplasty with predictable and consistent cement mantle. 5 to 7-Year results of prospective clinical and radiological assessment”. european Hip Society, 2006.

[2] Nieuwenhuis, Valstar, Persoon, De Wall malefijt, “The cone total hip prosthesis-subsidence and rotation. A radiostereometric analysis”. Hip International, 2006, Vol. 16 p. 138. european Hip Society.

[3] Heller mo, Bergmann G, Deuretzbacher G, Dürselen L, Pohl m, Claes L, Haas NP, Duda GN, “Musculo-skeletal loading conditions at the hip during walking and stair climbing”. J Biomech. 2001;34(7):883-93.

[4] Verdonschot N, Barink m, Stolk J, Gardeniers JWm, Schreurs BW, “Do unloading periods affect migration characteristics of cemented femoral components? An in vitro evaluation with the Exeter stem”. Acta orthop Belg. 2002;68(4):348-55.

[5] maher SA, Prendergast PJ, “Discriminating the loosening behaviour of cemented hip prostheses using measurements of migration and inducible displacement”. J Biomech. 2002;35(2):257-65.

[6] Cristofolini L, Teutonico AS, monti L, Cappello A, Toni A, “Comparative in vitro study on the long term performance of cemented hip stems: validation of a protocol to discriminate between “good” and “bad” designs”. J Biomech. 2003;36(11):1603-15.

proximal proximal

mid-stem level 3

17



Impact of cup design in reducing the risk of dislocation e. Spadinia, I. Quaglianaa, F. Siccardib, m. Bernardonic, m. Ponzonic

Introduction Dislocation remains one of the most common causes

of hip revision. Sariali et al. reports dislocation rates of between 0.5% and 10% for primary THA[1], increasing up to 10%-25% following revision surgery according to Alberton et al.[2]. In the United States hip instability has been classified, according to Bozic[3], as the most common reason for revision with an occurrence of 22.5%.

The treatment of dislocation following primary total hip arthroplasty is often expensive and these expenses have been quantified by Sanchez-Sotelo et al.[4] at approximately 19% of the hospital costs when compared to an uncomplicated total hip replacement. This expense rises to 148% in the case of revision surgery being required to solve the hip instability, highlighting the importance of preventing dislocation.

effective treatment of dislocation requires a thorough

Abstract Dislocation remains one of the most common causes of hip revision. Sariali reports dislocation rates of between 0.5% and 10% for primary THA, increasing to between 10% - 25% following revision surgery. The treatment following primary total hip arthroplasty is often expensive. In the case of revision surgery, this cost can be as high as 148% of the hospital costs when compared to an uncomplicated total hip replacement.Amongst the factors that can influence the risk of dislocation are prosthesis design features such as head-to-neck ratio, head diameter, femoral head offset and jumping distance. In particular, the jumping distance is used in this study as a predictive factor to evaluate the Versafitcup® Double mobility (medacta® International) effectiveness in the prevention of dislocation when compared with other prosthesis designs aimed as a solution for hip instability (cups with a design corresponding to a truncated hemisphere of 165°, such as m2a-magnum™ (BIomeT) and DUrom (Zimmer); dual mobility cups with a flat design or presenting an opening).The Versafitcup® Double mobility has been designed to maximize the effect by preventing hip instability. Thanks to its particular design, with the 5° raise, the Versafitcup® Dm has a larger jumping distance for all the sizes when compared to the other designs analyzed. For example, for heads (or liners in case of dual mobility design) size 48 we calculated the following jumping distance (JD) depending on the design: for Versafitcup® Dm the JD is 22.7 mm, for a dual mobility cup with a flat design JD is 20.2 mm, for a dual mobility cup with opening JD is 17.8 mm and for a m-o-m cup (truncated hemisphere of 165°) the JD is 15.8 mm. The Versafitcup® Double mobility is the design with the largest jumping distance.In conclusion we can confirm that the Versafitcup® Double mobility has a cup design that provides effective hip stability and has produced better theoretical results than other designs on the market. The numerical results are supported and validated by clinical studies demonstrating that, after 5 years (minimum) follow-up of over 120 patients, there were no dislocations, no cup migrations, no loosening and no detectable wear.

understanding of the cause. There are many factors that can influence the dislocation risk and these can be classified as three main types:

- Patient characteristics: important influencing aspects are abductor muscle efficiency, patient cooperation and neurological disease[1].

- The surgical technique: the following elements are all crucial to ensure hip stability during joint restoration – the centre of hip rotation, the femoral offset, the length of the lower limb and the correct anteversion angles. The hip approach is also an important factor, according to Sariali[1], the mean dislocation rate is significantly reduced using the anterior approach when compared to the posterior approach.

Impact of cup design in reducing the risk of dislocation


a. Medacta® International, Product Management department, Castel San Pietro, Switzerlandb. Medacta® International, Medical department, Castel San Pietro, Switzerlandc. Medacta® International, Research & Development department, Castel San Pietro, Switzerland

18



- The prosthesis design: head-to-neck ratio, head diameter, femoral head offset and jumping distance can all influence the risk of dislocation. Particularly the jumping distance is taken in this study as a predictive factor to evaluate the effectiveness of different cup design used as a solution for dislocation prevention. The jumping distance can be defined as the lateral translation (AB) of the femoral head centre required for dislocation to occur (Figure 1). The lower the jumping distance, the higher the theoretical risk of dislocation[6, 8].

F

A B

τψ

Figure 1. The jumping distance is the lateral translation (AB) of the centre of the femoral head (τ) before dislocation occurs. F is the load force and ψ is the planar cup inclination angle measured in the frontal plane[6].

There are currently different prosthesis designs to treat hip instability on the market:

- Large head: this kind of prosthesis is usually coupled with a truncated hemisphere of 165°, as m2a-magnum™ cup (BIomeT) coupled with metal large heads and DUrom cup (Zimmer). Printed results on the use of large head diameters in revision surgery[6] are controversial: studies still report a failure rate of between 8% and 40%, with no statistically significant difference between standard femoral head sizes (28, 32 mm) and large ones[7].

- Dual mobility design: the dual mobility concept is a common solution to avoid hip instability. Published clinical results show extremely low dislocation rates for dual mobility cups, as low as 0.1% in over 1000 registered patients[9]. For dual mobility concept, various shapes have been developed such as: a truncated hemisphere of 165°, as m2a-magnum™ cup (BIomeT) coupled with dual mobility liner; cups with a flat design; prosthesis with an opening; elliptic cups with a raise as the

Versafitcup® Double mobility (Versafitcup® Dm, Figure 2) by medacta®. The Versafitcup® Dm has been especially designed to optimise the design factors that influence hip stability. The Versafitcup® Dm design originates from Prof. Bousquet concept who has more than 30 years of clinical experience[12].

The aim of this study is to evaluate the effectiveness of Versafitcup® Dm against dislocation through comparison with different cup designs, using jumping distance as a predictive factor.

5° Raise for additional cover

Figure 2. Versafitcup® Dm (Double mobility) by medacta®.

material and methods The jumping distance is defined by Sariali et al.[6]

through the formula below:

(π/2)-ψ-arcsin (offset/R)2JD = 2R sin

Where:- JD: Jumping Distance;- r: head radius;- ψ: Planar cup inclination angle measured on X-Rays;- offset: offset of the femoral head, defined as the distance between the femoral head centre and the cup opening plane (Figure 3).

Figure 3. offset and inset of the femoral head. For reference, if the femoral centre is located inside the cup, the offset is negative and the absolute value is called femoral inset, whereas if it is situated outside the cup the offset is positive.


19



In the case of a dual mobility cup the main component for hip stability is not the femoral head, but the mobile liner, which acts as a large head inside the cup. For this reason the parameters used throughout the calculations are the ones relating to the mobile liner and not the ones relating to the femoral head.

The jumping distance has been evaluated for the following designs: Versafitcup® Dm by medacta® (a); flat dual mobility cup (b); dual mobility cup with opening (c); truncated hemisphere of 165° (d), such as m2a-magnum™ cup (BIomeT) coupled with metal large heads or dual mobility liners, and DUrom cup (Zimmer) coupled with metal large heads; ceramic-on-ceramic THr provided by CeramTec (e). Consider the planar cup inclination angle (ψ) has been fixed at 45°, which corresponds to a standard cup inclination in a total hip replacement.

a) Versafitcup® Dm: the jumping distance has been calculated for the whole Versafitcup® Dm product range, from size 46 mm, with a liner external diameter of 38 mm to size 64 mm, with a liner external diameter of 56 mm (the cup design is reported in Figure 4). This design shows an offset of -4.0 mm.

-4.0 mm

Figure 4. offset of Versafitcup® Double mobility Liner.

b) Flat dual mobility cup: this cup design has been obtained by removing the 5° raise from the original Versafitcup® Dm. The result is reported in Figure 5. The jumping distance has been calculated for a product range concurrent with the one of Versafitcup® Dm (sizes from 46 mm to 64 mm, with liner diameter ranging from 38 mm to 56 mm). This design shows an offset of -1.1 mm.

-1.1 mm

Figure 5. offset of a flat dual mobility cup design.

c) Dual mobility cup with opening: this cup design has been obtained by removing the raise and additional lateral zone from the original Versafitcup® Dm. The result is reported in Figure 6. The jumping distance has been calculated for a product range concurrent with the one of Versafitcup® Dm (sizes from 46 mm to 64 mm, with liner diameter ranging from 38 mm to 56 mm). This design shows an offset of +1.5 mm.

+1.5mm

Figure 6. offset of a dual mobility cup design with opening.

d) Cup design corresponding to a truncated hemisphere of 165°: this cup design (see Figure 7) is evident in various cups on the market, such as m2a-magnum™ (BIomeT)[10], coupled with both metal large heads and dual mobility liners, and DUrom (by Zimmer) coupled with metal large heads. The product range analyzed has head sizes of 40 mm, 44 mm, and 48 mm. The jumping distance of this design has been calculated by Sariali et al.[6], and reports an head offset of about 3 mm.

OFFSET A

165˚

O

Figure 7. offset of a cup design corresponding to a truncated hemisphere of 165°.

e) Ceramic-on-ceramic THr: this design corresponds to a standard ceramic-on-ceramic coupling currently on the market, provided by CeramTec. The product range analyzed has head sizes of 28 mm, 32 mm, 36 mm, and the data for the offset was provided by Sariali et al.[6]. The heads of 28 mm and 32 mm diameter have an inset of 1 mm, whereas the heads of 36 mm diameter have an offset of 0 mm. This design has been analyzed to provide an example of a standard total hip replacement, even if it is not commonly used to treat hip instability.


20



results The evaluation of jumping distance for Versafitcup®

Double mobility is reported in Table 1.

Versafitcup® Dm cup size

(mm)

Liner diameter

(mm)

radius (mm)

offset (mm)

Jumping Distance

(mm)46 38 19 -4.0 18.748 40 20 -4.0 19.550 42 21 -4.0 20.352 44 22 -4.0 21.154 46 23 -4.0 21.956 48 24 -4.0 22.758 50 25 -4.0 23.560 52 26 -4.0 24.362 54 27 -4.0 25.164 56 28 -4.0 25.9

Table 1. evaluation of Jumping distance for Versafitcup® Double mobility.

The jumping distance for Versafitcup® Dm ranges from 18.7 mm to 25.9 mm.

The same calculation has been used for the flat dual mobility cup, reported in Table 2, and for dual mobility cup with opening design, reported in Table 3.

Flat Dual mobility cup

size (mm)

Liner diameter

(mm)

radius (mm)

offset (mm)

Jumping Distance

(mm)46 38 19 -1.1 16.248 40 20 -1.1 17.050 42 21 -1.1 17.852 44 22 -1.1 18.654 46 23 -1.1 19.456 48 24 -1.1 20.258 50 25 -1.1 21.060 52 26 -1.1 21.862 54 27 -1.1 22.664 56 28 -1.1 23.4

Table 2. evaluation of Jumping distance for a flat dual mobility cup design.

The jumping distance for a flat dual mobility design ranges from 16.2 mm to 23.4 mm.

Dual mobility cup with

opening size (mm)

Liner diameter

(mm)

radius (mm)

offset (mm)

Jumping Distance

(mm)

46 38 19 1.5 13.848 40 20 1.5 14.650 42 21 1.5 15.452 44 22 1.5 16.254 46 23 1.5 17.056 48 24 1.5 17.858 50 25 1.5 18.660 52 26 1.5 19.462 54 27 1.5 20.164 56 28 1.5 21.0

Table 3. evaluation of Jumping distance for a dual mobility with opening cup design.

The jumping distance for a dual mobility design with opening ranges from 13.8 mm to 21.0 mm.

These results are in line with the ones reported by Sariali et al.[6], which claim that the jumping distance increases as the femoral head (or liner in case of dual mobility) diameter increases (maintaining as constant the cup inclination angle and the offset).

The calculation of the jumping distance of different dual mobility cup designs has now been compared with the jumping distance of other designs currently on the market and reported upon, such as: ceramic-on-ceramic THr provided by CeramTec; cups with a design corresponding to a truncated hemisphere of 165° (m-o-m), such as m2a-magnum™ (BIomeT)[10] and DUrom (Zimmer)[6]. The results of the comparison are reported in Figure 5. The Versafitcup® Dm has a larger jumping distance for all sizes compared not only with Ceramic-on-Ceramic system by CeramTec, but also with cups with a design corresponding to a truncated hemisphere of 165°, such as m2a-magnum™ (BIomeT) coupled with dual mobility liners and metal large heads and DUrom (Zimmer) coupled with metal large heads. For example, for heads (or liners in case of dual mobility design) size 48 mm we have the following jumping distance, depending on the design: for Versafitcup® Dm the JD is 22.7 mm, for a dual mobility cup with a flat design JD is 20.2 mm, for a dual mobility cup with opening JD is 17.8 mm and for a m-o-m cup (truncated hemisphere of 165°) the JD is 15.8 mm. This example demonstrates that by reducing the cup cover the jumping distance is decreased. moreover, the jumping distance decreases as the offset increases.


21



565452

a) Versafitcup® Dm

b) Dual mobility Flat Design

c) Dual mobility Design with openining

d) Truncated hemisphere of 165˚

e) C-o-C THr

30

25

20

15

10

5048464442403822 363228

Figure 5. Comparison of Jumping distance of different cup designs. In the horizontal axis the liner diameter is considered in the case of dual mobility design, the head diameter is used in the other cases. In the vertical axis, values of the jumping distance are listed.

Discussion and conclusionThe Versafitcup® Dm design guarantees a high jumping

distance which can be defined as the degree of lateral translation of the femoral head centre that is required for dislocation to occur. The lower the jumping distance, the higher the theoretical risk of dislocation.

It is important to note that the jumping distance of Versafitcup® Dm is larger not only in comparison with smaller heads (Ceramic-on-Ceramic THr) but with other cup designs with similar head diameters (in the case of a dual mobility cup the mobile liner acts as a large head in terms of joint stability). So, to reduce the risk of dislocation, the head diameter and the head offset parameters must both be taken into account. Another parameter that plays an important role for the hip stability is the cover level of the cup. It has been demonstrated that reducing the cup cover on the dual mobility liner has a negative effect on the jumping distance, which is a predictive factor of the risk of dislocation. These results are reached due to the technical features of the Versafitcup® Dm cup:- dual mobility design, where the real responsible for hip stability is the liner diameter and not the head diameter;- 5° raise, which increases the cover surface of the cup on the liner in the posterior part and enhances the inset value as a result; - an offset of -4 mm, reducing the risk of dislocation when compared to other designs currently on the market.

In conclusion, the Versafitcup® Double mobility has

a cup design that provides increased hip stability and has produced better theoretical results than other designs on the market. The numerical results are supported and validated by clinical studies demonstrating that, after 5 years (minimum) follow-up of over 120 patients, there were no dislocations, no cup migrations, no loosening and no detectable wear[11].

references[1] Sariali e, Leonard,P, mamoudy P. “Dislocation after total hip arthroplasty using Hueter anterior approach.” J Arthroplasty 2008; 23 (2): 266-72.[2] Alberton G, High W A, morrey B F. “Dislocation after revision total hip arthroplasty: An Analysis of risk factors and treatment options”. J Bone Joint Surg (Am) 2002; 84: 1788-92.[3] Bozic KJ. “The increasing number of THA revisions in the United States: Why is it happening?” orthopedics Today 2009; 29:6. october 2009.[4] Sanchez-Sotelo J, Haidukewych GJ, Boberg CJ. “Hospital Cost of Dislocation After primary Total Hip Arthroplasty.” J Bone Joint Surg, 2006 Feb, 88(2):290-4.[5] Jolles B m, Zangger P, Leyvraz P F. “Factors predisposing to dislocation after primary total hip arthroplasty. Multivariate analysis.” J Arthroplasty 2002: 17: 282-8.[6] Sariali e, Lazennec JY, Khiami F, Catonné Y, “Mathematical evaluation of jumping distance in total hip arthroplasty.” Acta orthopaedica 2009; 80 (3): 277-282. [7] Kung P, riers m D. “Effect of femoral head size and abductors on dislocation after revision THA”. Clin orthop 2007; (465): 170-4. [8] Blumenfeld TJ, Bargar WL. “Use of larger femoral heads in revision total hip arthroplasty: will this solve dislocation?” orthopedics october 2008; 31(10):995.[9] S. Leclercq, S. el Blidi, J.H. Aubriot, “Treatment of recurrent dislocation of Total Hip Replacement using Bousquet type double mobility cup.” review of 13 cases, revue de Chirurgie orthopédique, 81, 389-394, Service de Chirurgie orthopédique et Traumatologique, CHr Côte de Nacre, Caen, France.[10] “Design Affects Performance of Metal-on-Metal Constructs.” BIomeT orthopedics, Form No. BoI0325.0 reV063011.[11] P. Laffargue, Versafitcup® “Double Mobility cup: outcomes at a mean follow-up of 5 years.” eForT 2011, June 1st to 4th, Copenhagen (DK).[12] G. Bousquet et al. “results with a cementless alumina coated cup with a dual mobility, a twelve years follow-up study.” Int orthop. 1998; 22(4) : 219-224.


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Abstract errors in surgical technique and small changes in component positioning compromise postoperative performance of a prosthesis, potentially decreasing implant survival. A patient-matched approach to total knee arthroplasty, when compared to the traditional approach, should show improvements which are potentially beneficial to both surgeon and patient. The main purpose of the myKnee® patient-matched instruments is to provide 3D pre-operative planning for a total knee replacement and create anatomical cutting blocks which are reproduced from CT or mrI scans of each individual patient.This should provide easier and more stable positioning of the cutting block, more accurate positioning of components and improve patient satisfaction as a result of reduced surgical stress. The data collected from 155 myKnee® cases shows this system provides accuracy. The difference between the planned and the performed resections was on average less than 0.8 mm. recuts were not required in the majority of cases. The size matching, between the planned and the actual component implanted, was shown to be accurate, particularly the femoral component with only one size error recorded in 5% of cases. This data confirms the precision of the system and potential increase in prosthesis survival. The surgeons were completely satisfied with the technique in 97% of cases and confirmed cutting blocks were easily positioned and felt stable.

Preoperative planning accuracy of myKnee® systemm. Dussaulta, T. Goldbergb, r. Greenhowc, D. Hamptond, S. Parrye, m. Slimackf

Preoperative planning accuracy of myKnee® system


IntroductionThe main purpose of the myKnee® patient-matched

instruments (medacta® International, Switzerland) is to use the patient’s CT scan or mrI to provide 3D pre-operative planning for a total knee replacement and create anatomical cutting blocks which are specific to the individual patient’s anatomy. The positioning of the cutting blocks will be based on the anatomical landmarks shown in the CT or mrI.

Potentially, the advantages of the patient specific instrumentation include: a) precise positioning of the implant, potentially resulting in an increase in prosthesis survival [1]; b) absence of intramedullary canal violation, decreasing the risk of embolism and blood loss[2, 3]; c) reduction in surgical steps for bone resection and length of surgery; d) reduced time for sterilization and instrument preparation, potentially increasing number of surgeries per session [8]; e) reduction of the costs associated with sterilization of instruments.

Clinical evidence of accuracy and effectiveness of the myKnee® system is reported in different studies, evaluating it on the basis of accurate implant positioning[4, 5, 6, 7]

and time and cost savings[8, 9]. All these studies reported better postoperative mechanical alignment than those obtained in conventional procedures. They were also consistent with the results gained with navigation system. As fewer instruments are needed to perform the surgery, there are economical advantages, which include reduced

preparation time in the operating room and instrument sterilization, resulting in lower costs. Goldberg reported an additional 2 cases per week resulting in increased hospital profits of 230000$/year[8]. other surgeons feel that the procedure takes less time and is more efficient as reported by Koch’s in a series of 56 TKAs[9].

Limited literature has been published on the different patient-matched knee instrumentations available in the market. The results of these publications are debatable as they mainly report on accuracy of postoperative knee alignment[10- 15] and show an accuracy which is similar to or not as good as those achieved in conventional procedures. All these systems are mrI-based, so the lack of accuracy, reported in some studies, may be due to the limitations in the ability of the technology to precisely define the joint model. The mrI technology is more time consuming and could result in movement artifact that cannot be easily detected.

The main topic of the study focused on the preoperative accuracy in the planning phase of the myKnee® system. Baldo reported preliminary results on a small group of patients, showing perfect preoperative reliability[5].

a. Aurora Memorial Hospital, Burlington - USAb. North Austin Medical Center, Austin - USAc. Peak Orthopaedics and Spine, Colorado - USAd. Pampa regional medical center, Texas - USAe. Dixie Regional Medical Center, Utah - USAf. UHS- Kenosha, Wisconsis - USA

23



The aim of this study is to evaluate the accuracy of the preoperative planning from a multicentric collection of data, reporting on the experience with the myKnee® system based on technical data collected during surgeries and the surgeons thoughts regarding this new practice.

General dataBetween January 2010 and January 2011, 155 TKA

procedures were carried out, in six centers, using the CT based myKnee® system. The GmK® Primary knee prosthesis (medacta® International, Switzerland) were implanted in all patients: 72 on the left side and 83 on right side. The mean age of the patients was 66 years (range: 41-97 years).

A CT scan of the knee is obtained around 1 month prior to the surgery. The myKnee® cutting blocks and the 3D bone models are manufactured using a Selective Laser Sintering (SLS) technique. The positioning and the design of the myKnee® cutting guides are devised using dedicated software, designed by medacta® International.

The performance of the myKnee® system was investigated by comparing preoperative planning and actual intra-operative performance.

The analysis was based on the following data, which were collected preoperatively and postoperatively: six intraoperative resections (distal medial and lateral femoral resections, posterior medial and lateral femoral resections, medial and lateral tibial resections), femoral and tibial components size, Pe insert thickness, the necessity for femoral and/or tibial recuts. In addition, the surgeons were asked to complete a questionnaire on their thoughts about the cutting guides (how they matched the knee and how comfortable to use), their expectations and the stability of the knee postoperative.

The size matching was evaluated by comparing planned and implanted size of femoral and tibial components.

Statistical AnalysisDescriptive analysis was performed using univariate

statistics for the continuous variables and frequency distribution for the categorical variables.

results By analysis of mechanical axis alignment, 111

patients reported varus pre-operative deformities, with a mean mechanical alignment of 174.2° (range 166.5°-179°) and 34 subjects had pre-operative valgus deformities averaging 184.8° (range 180.5°-191.5°). 6 patients reported a neutral alignment (180°).

The mean actual and planned distal medial femoral resections were 8.2 and 9 mm respectively, the distal lateral femoral resections 6.9 and 6.6 mm respectively, the posterior medial femoral resections 8.5 and 8.9 mm respectively and the posterior lateral femoral resections 6.8 and 6.5 mm respectively. moreover, the mean actual and planned tibial resections were medially 5.2 and 5.8 mm respectively and laterally 8.1 and 7.9 mm respectively.

The size matching, for both femoral and tibial components, was satisfactory, the mismatched cases reported are a maximum of one size. The number of mismatches decrease as the surgeon conquers his learning curve and becomes more confident with the technique and the personal myKnee® technician assigned to him. Likewise, the myKnee® technician, becomes more familiar with the surgeon’s expectations, resulting in more personalized pre- op planning. In fact we noted a decrease in the mismatch of the tibial size from 68% to 86% when comparing the number of cases done by each surgeon, which were temporally ordered and divided into first and second half groups. There was no decreasing trend for the femoral component however, the mismatched cases were few and equally divided in the two groups (Figures 1 and 2).

Femoral component (n=77)

dist

ribu

tion

[%]

Figure 1. Femoral size matching for second group.


24



Tibial component (n=77)

dist

ribu

tion

[%]

Figure 2. Tibial size matching for second group.

Figure 3 shows the distribution of Pe insert thicknesses. The first three thicknesses covered 94% of cases, as reported for a conventional total knee arthroplasty surgery[16].

PE insert thickness (n=137)

dist

ribu

tion

[%]

[mm]

Figure 3. Pe Insert thickness distribution.

The percentage of recuts performed during surgery is summarized in Table 1. The thickness of recuts reported ranges from 2 to 4 mm.

Femoral distal recuts

Femoral posterior

recutsTibial recuts

none 98.5% 100% 87.8%2mm 0.7% 0% 8.6%4mm 0.7% 0% 3.6%

Table 1. Femoral and tibial recuts.

The questionnaire results showed that surgeons were completely satisfied (97% cases) with myKnee® performance. They reported accurate matching with cutting guides and the anatomical knee in 90% of cases and consequently easy positioning of cutting blocks which felt stable. Knee stability was achieved postoperatively in 100% of patients.

Discussion The perioperative experience with the patient-matched

technique was positive. The results showed accuracy in the procedure, evaluated on the basis of intraoperative resections, size matching and recut requirements. The intraoperative resections reflected the pre-operative planning, ensuring a mean difference between the two measures below 0.8 mm, demonstrating accurate positioning of the cutting blocks and good reproduction.

The results of the size matching analysis were also very satisfactory. Some cases reported an increase or decrease of one size in both tibial and femoral component, with a higher incidence in the tibial component, possibly due to the presence of posterior osteophytes[17]. During planning it is difficult to distinguish by coronal radiographic images, the boundary between actual tibial bone edge and the ostheopytes and therefore to define the tibial size precisely. The mismatch of tibial components are in line with the higher rate of tibial recuts and decrease as the surgeon conquers his learning curve and his confidence increases with the technique and the personal myKnee® technician assigned to him. In the light of these results, the patient-matched knee replacement system certainly provides benefits. These include reduced trauma to the knee as a result of more precise cuts and no intramedullary violation. Furthermore, studies on the myKnee® system have shown that surgery is more time efficient with less effort required for accurate implant positioning, resulting in restored knee alignment postoperatively. This should result in more favorable implant endurance and in fact it has already been shown that mechanical axis within a range of ±3° varus/valgus gives better long term clinical outcomes[1, 18].

Conclusion The myKnee® procedure can be considered accurate

and safe with no adverse events reported. The negligible difference between the planned and actual resections (less than 0.8 mm in average) demonstrate that myKnee® cutting block positioning is a straightforward procedure resulting from good pre-operative planning reproduction.

The good size matching for both femoral and tibial side prove the reliability of size estimation of the myKnee® preoperative planning. Finally, the questionnaires collected confirm these results, showing the high rate of satisfaction expressed by the surgeons about the myKnee® system and more particularly, postoperative stability of the knee in 100% of cases. In conclusion, myKnee® patient-matched instrumentation is a novel technique which potentially offers increased accuracy and effectiveness during surgical implantation of TKA.


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references[1] ritter mA, Faris Pm, Keating em, meding JB,“Postoperative alignment of total knee replacement: its effect on survival”. Clin orthop. 1994; 299:153-156.

[2] Kalairajah Y , Cossey AJ, Verrall Gm, Ludbrook G, Spriggins AJ, “Are systemic emboli reduced in computer-assisted knee surgery? A prospective, randomised, clinical trial”. J Bone Joint Surg Br. 2006, 88 (2): 198-202.

[3] Kalairajah Y, Simpson D, Cossey AJ, Verrall Gm, Spriggins AJ, “Blood loss after total knee replacement: effects of computer-assisted surgery”. J Bone Joint Surg Br. 2005;87(11):1480-2.

[4] Leon V “Patient matched technology vs conventional instrumentation and CAS”. Podium presentation at the 6th m.o.r.e International symposium, Stresa, Italy, may 13-14, 2011.

[5] Baldo F, Boniforti B, “Patient-specific cutting blocks for total knee arthroplasty: preoperative planning reliability”. J. orthopaed Traumatol 2011; 12: S23-S88.

[6] müller DA, meyer D, Koch P, “CT based patient-specific cutting blocks for total knee arthroplasty: technique and preliminary radiological results”. Podium presentation at the 71th Annual Congress of the SSoT, Lausanne, Switzerland, June 22-24, 2011.

[7] Koch P, müller DA, Fucentese SF, “Guide de coupe sur mesure pour PTG: presentation de la technique opératoire et resultants radiologiques preliminaries”. Podium Presentation at the 86th Annual Congress of the SoFCoT, Paris, France, November 7-11, 2011.

[8] Goldberg TD “MyKnee® economical and clinical results”. Podium Presentation at the 6th m.o.r.e International symposium, Stresa, Italy, may 13-14, 2011.

[9] Koch P “MyKnee® system: A new vision in total knee replacement”. Leading opinions-orthopädie & rheumatologie 2011, 2: 32-35.

[10] Webb J, Beaver r, Harvie P, Sloan K, “Early experience with customized patient instrumentation in knee arthroplasty”. Podium presentation at the 12th eFForT congress, Copenaghen, June 1-4, 2011.

[11] Parker D, Kinzel V, Scholes C, Giuffrè B, Coolican m, “Evaluation of the Visionaire instrumentation for total knee arthoplasty using computer navigation”. Podium Presentation at the AoA NZoA meeting, rotorua, New Zeland, october 9-14, 2011.

[12] Noble JW, moore CA, Liu N, “The value of patient-matched instrumentation in total knee arthroplasty”. J. Arhroplasty 2012, 27(1): 153-155.

[13] misur P, Strick N, Puna r, “The accuracy of implant positioning using the Visionaire patient matched knee arthroplasty system”.Podium presentation at the AoA NZoA meeting, rotorua, New Zeland, october 9-14, 2011.

[14] Klatt BA, Goyal N, Austin mS, Hozack WJ, “Custom-Fit Total Knee Arthroplasty (OtisKnee) Results in Malalignment”. J. Arthroplasty 2008, 23(1):26-29.

[15] Ng VY, DeClaire JH, Berend Kr, Gulick BC, Lombardi AV, “Improved accuracy of alignement with patient-specific positioning guides compared with manual instrumentation in TKA”. Clin orthop relat res 2012, 470(1):99-107.

[16] medacta® file.

[17] Wluka Ae, Wang Y, Davis Sr, Cicuttini Fm, “Tibial plateau size is related to grade of joint space narrowing and osteophytes in healthy women and in women with osteoarthritis”. Ann rheum Dis 2005, 64:1033-1037.

[18] Ishida K, matsumoto T, Tsumura N, Kubo S, Kitagawa A, Chin T, Iguchi T, Kurosaka m, Kuroda r, “Mid-term outcomes of computer-assisted total knee arthroplasty”. Knee Surg Sports Traumatol Arthrosc 2011 (epub ahead of print).


26




Cadaver test and mrI kinematic study of the flat lateral and congruent lateral tibial inserts of the GmK® Sphere implant

Cadaver test and mrI kinematic study of the flat lateral and congruent lateral tibial inserts of the GmK® Sphere* implant V. Pinskerovaa, m. Freemanb,c,d

Flat lateral version 1. The enhanced medial stabilizer

The enhanced medial stabilizer was designed by Freeman and others in the 1980s as a modification of the F/S prosthesis (Protek AG). The modification consisted of making the medial articular surfaces spherical instead of cylindrical with a higher (11mm) anterior lip. The anterior and posterior lips, working in combination, provided A-P stability throughout the range of motion whilst the spherical shape permitted tibial-femoral rotation around a medial axis (as in the natural knee). The modified prosthesis was patented by Finsbury Instruments and marketed in two slightly different forms by Finsbury Instruments (as the mrK) and by Wright medical Technology (as the medial Pivot). These prostheses were inserted after the division of both cruciate ligaments.

In the 1990s, the anatomy and kinematics of the normal knee were not fully understood and the prostheses continued to have anterior and posterior lips laterally. However, from 1997 onwards the anatomy has been studied by Pinskerova, Freeman and others[1-16]. Fortunately (in view of the medial re-design described above) it was found that the normal knee, like the modified prosthesis, was antero-posteriorly stable medially. In contrast it was found that the normal knee was NoT A-P stable laterally: the LFC (lateral femoral condyle) is able to move relative to the tibia by about 20 mm A-P. This finding raised the question: should the

Abstract Total Knee replacement with a condylar prosthesis and the division of both cruciate ligaments was first proposed and carried out by Freeman. The operation was popularised particularly by Insall. In order to prevent the anterior or posterior femoral subluxation which was anticipated (on theoretical grounds) as a possible complication of this operation, the tibial components were designed with anterior and posterior polyethylene lips on both tibial condyles to check femoral translation. Today, most tibial components have anterior and posterior lips, on both tibial condyles. We have studied the effect of removing the anterior and posterior lateral tibial lips in combination with a re-designed medial compartment providing enhanced anterior-posterior (A-P) stability.

lateral tibial lips be retained in the prosthesis? Hence the prosthesis has been re-designed by removing 1) the posterior lateral lip and 2) the anterior and posterior lateral lips. This has been done in prostheses having the additional stabilizing mechanism medially.

2. The posterior lip

The posterior lip might have the function of preventing the femur from undergoing excessive posterior translation. However since the LCL (lateral collateral ligament) is about 7 mm lax at 90dg it is theoretically possible for a prosthetic LFC to “jump“ a posterior lip up to 7 mm in height. A lip of this height or higher is impractical since it would interfere with flexion. In any event the clinical A-P instability which is sometimes seen with the F/S prosthesis takes the form of excessive posterior (not anterior) tibial translation.

The effect of removing the posterior lip has been studied using mrI in cadaver knees with polymeric components (VP prosthesis). It was found (see Figure 1) that the femur moved backwards in a normal fashion with flexion but did not dislocate posteriorly (nor in any other way). Prostheses for clinical use were then manufactured by Finsbury Instruments Limited and received a Ce mark in 2008. Ten such prostheses have been implanted by mr G. Scott at the royal London Hospital. No femur

a. First Orthopaedic Clinic, Charles University, Prague, Czech Republic b. Institute of Orthopaedics and Musculoskeletal, University, College, 79 Albert Street, NW1 7LX London, UKc. School of Engineering Sciences, Southampton University, Southampton, UKd. The Royal London Hospital, London, UK

*The GmK® Sphere is not FDA cleared

27



has dislocated posteriorly and clinically the results are the same as those for the prosthesis with the posterior lip (the mrK, first known as the F/S 1000).

We conclude that the lateral posterior lip is not necessary with the new medial geometry as described. Both cruciate ligaments were excised for the mrK and the VP prosthesis.

EXT 45dg 90dg 120dg

lat

med

Figure 1. mrI of a VP prosthesis without posterior lip implanted in a cadaver. medial and lateral side in extension and at different degrees of flexion.

3. The anterior lip

We have not studied the isolated removal of the anterior lip. But we have studied in the cadaver and in models the effect of removing the anterior lip as well as the posterior lip laterally. In these studies the medial geometry remained as described above and both cruciate ligaments were removed (with one exception described below). our observations were as follows:

1) In one cadaver knee a VP prosthesis was cemented in place and the anterior lip was then progressively shortened by removing its posterior extremity in three stages (Figure 2).

Findings - It was found that, as in the normal knee, the LFC moved anteriorly with extension. Thus the LFC only made contact with the anterior lip in full extension, the anterior lip has no function as soon as the knee is flexed. When a small portion of the posterior extremity of the anterior lip was removed the LFC moved a little further forwards in full extension. When a second portion of the anterior lip was removed the LFC did not move further forwards and did not contact the remaining anterior lip in full extension. When the whole of the anterior lip was removed a gap remained between the curved articular surface of the LFC and the flat surface of the tibia in full extension. The LFC did NoT articulate more anteriorly

with the tibial component because it was held back (as in the normal knee) by the tense and oblique LCL (see Figure 9a below).

Second step ofshortening

First step ofshortening

Original ant lip

No ant lip

(ant vertical tibial mark shows positionof femoral mark instep 2. There is nowa gap above this mark)

Figure 2. VP prosthesis implanted in cadavers. The anterior lip was progressively shortened in three stages.

Summary - The anterior lip can function (if at all) only in full extension but in practice it has no function even in the absence of the cruciate ligaments provided the LCL is present. We emphasize that the normal tibia does not have an anterior lip: indeed it has an anterior recess which receives the anterior horn of the meniscus in extension (Figure 3).

Figure 3. mrI and photo of the lateral side of a cadaveric knee: the normal tibia does not have an anterior lip. Indeed it has an anterior recess which receives the anterior horn of the meniscus in extension.


The GmK® Sphere is not FDA cleared

28



2) A second cadaver implantation was carried out with a polymeric prosthesis made without a posterior nor an anterior lateral lip. The result was the same as in the fully excised anterior lip described above (Figure 4).

Figure 4. Cadaver implantation performed with a polymeric prosthesis made without a posterior nor an anterior lateral lip. Photos in full extension and at different degrees of flexion.

3) A third cadaver implantation was made with the same type of prosthesis as in paragraph 2 above. In this operation it was intended to excise both the ACL and the PCL as had been done previously. The ACL was excised but in error the PCL was divided but not excised (Figure 5).

Figure 5. PCL cut at its tibial attachment but not excised. The red arrow shows where the PCL was divided.

In this knee the behaviour of the lateral compartment during flexion was as described above. From 0dg to 90dg the medial femoral condyle remained centrally located in the medial tibial sphere (Figure 6).

Med Lat

Figure 6. mrI of a cadaver implantation of a polymeric prosthesis made without a posterior nor an anterior lateral lip. medial and lateral side in full extension and at 90dg of flexion.

However at 120dg when the posterior closing part of the medial femoral radius had entered the tibial sphere, the femoral condyle moved posteriorly 7 mm. However it remained in the tibial sphere: it did not sublux (Figure 7).

Figure 7. mrI of a cadaver implantation of a polymeric prosthesis made without a posterior nor an anterior lateral lip. medial (left) and (right) compartments at 120dg. medially the centre of the femoral sphere has moved back 7mm. The femoral sphere remains within the tibial sphere.

examining the knee visually showed that the medial side behaved in this way at 120dg and 150dg but mrIs were not made at 150dg of flexion.

Later review of the mrIs showed the presence of a residual and possibly functioning PCL which had not been appreciated at the operation (Figure 8).


90dg

EXT

45dg

120dg

patella reducedobscuringlateralcompartment

90dg

EXT

prosthesisuncemented


29



Figure 8. red arrow showing remaining PCL.

4. Study of a Knee model

b) 90dga) EXT

d) 120dgc) 120dg

Figure 9. a) Articulated model implanted with the flat lateral tibial prosthesis. Lateral view in full extension. The femur is fully anterior in full extension but still does not contact the tibia at its anterior extremity (red arrow). Forward movement of the femur moves the femoral attachment of the LCL anteriorly and thus limits further forward movement. As a consequence the LCL becomes oblique and tense (green arrow). The PCL (blue arrow) has been left slightly more lax than normal. b) The femoral component (medial femoral condyle) is central within the tibial sphere. c) The femoral component has now moved 5mm posteriorly within the tibial sphere. The PCL (not seen) is tense. d) The femur has

now been externally rotated bringing the attachments of the PCL (not seen) closer together. The femoral component can now move forwards to be central in the tibial sphere.

In a model of the replaced knee (Figure 9a: lateral view in full extension, Figures 9b-d: medial view in flexion) it was then found that a tight PCL at 120dg had the effect of drawing the medial femoral condyle posteriorly (Figure 9c). When the flexed knee in the model was externally rotated (Figure 9d) this displacement did not occur because the femoral and tibial attachments of the PCL were moved towards each other by external femoral rotation.

5. Re-examination of the replaced knee

Finally we re-examined the 2 replaced knees to determine the status of the PCL in the flat lateral knee and the cause of limited flexion in the congruent knee.

The technique used to defunction the PCL had been that employed clinically in Prague, namely to cut the ligament at its tibial attachment. on re-examination it was found that the normal adhesions between the PCL, the synovium and the femur had had the effect of keeping the two ends of the cut ligament in contact during flexion/extension. This finding confirmed the appearances on mrI. When the PCL was entirely resected, the replaced knee flexed to 130dg without backward movement of the femur (Figure 10). This confirmed our finding in the model. We conclude that if the PCL is to be defunctioned reliably, it should be excised, not merely divided, as described by Freeman and Samuelson (operative Technique for the F/S knee. Protek Ag).

Figure 10. At 130dg flexion after excision of the PCL the medial femoral condyle does not move back.



30



6. Conclusion

In the cadaver knee replaced with a prosthesis, a small lateral anterior lip appears to have no function. It is possible to insert a prosthesis having neither anterior nor posterior lips with resection of both cruciate ligaments. If the PCL is retained: the medial femoral condyle may either move posteriorly within the tibial sphere at 120dg or the femur may externally rotate around the medial sphere. It is not clear which might be preferable clinically.

0

Interrupted line after PCL resection

EXT306090

120

M4 Flat

Medialmm

Lateralmm

50

40

30

20

10

0

30

20

10

0

47 mm

Figure 11. Graphic showing the top of the tibia of a cadaver knee replaced with the flat lateral prosthesis.

Congruent lateral version

1. Report on the congruent prosthesis

one knee was replaced uneventfully with the congruent prosthesis. However when mrIs were taken with the patella reduced and the wound sutured, the knee could not be flexed beyond 90dg. From 0dg to 90dg the mrIs were as expected (see Figure 12).

Lat

Med

EXT 90dg 90dg

Figure 12. mrIs of the congruent replacement in extension and at 90dg flexion. Photo (top right) at 90dg of flexion.

2. Re-examination of the congruent prosthesis forlimited flexion

The specimen had originally been removed from the cadaver by an anatomy technician. The femur was cut about 15 cm above the knee. Just below this level the thigh muscles had been kept in place by tying them tightly to the femur with an encircling piece of string. The string was not noticed when the knee was replaced.

When the knee was re-examined, the string was noticed and divided. This released what were effectively “adhesions” between the femur and the quadriceps muscle. The replaced knee now flexed to 145 degrees without backward movement of the medial femoral condyle (Figure 13). We did not have the opportunity to carry out additional mrIs in deep flexion.

Figure 13. Congruent knee after the string was divided. The knee now flexed to 145dg without posterior movement.

3. Conclusion

Limited flexion was due to an oversight on our part (failure to remove string used in preparation of the specimen). The prosthesis otherwise moved correctly (Figure 14).

EXT306090

M4 Congruent

Medialmm

50

40

30

20

10

0

30

20

10

0

47 mm

Figure 14. Graphic showing the top of the tibia of a cadaver knee replaced with the congruent lateral prosthesis.



31



references[1] Pinskerova V, Iwaki H, Freeman mA, “The shape and relatives movement of the femur and tibia at the knee”, orthopade, 2000.

[2] Pinskerova V, maquet P, Freeman mA, “Writings on the knee between 1836 and 1917”, JBJS Br, 2000.

[3] Iwaki H, Pinskerova V, Freeman mA, “Tibiofemoral movement 1: the shapes and relative movements of the femur and tibia in the unloaded cadaver knee”, JBJS Br, 2000.

[4] Hill PF, Vedi V, Williams A, Iwaki H, Pinskerova V, Freeman mA, “Tibiofemoral movement 2: the loaded and unloaded living knee studied by MRI”, JBJS Br, 2000.

[5] Nakagawa S, Kadoya Y, Todo S, Kobayashi A, Sakamoto H, Freeman mA, Yamano Y, “Tibiofemoral movement 3: full flexion in the living knee studied by MRI”, JBJS Br, 2000.

[6] Karrholm J, Brandsson S, Freeman mA, “Tibiofemoral movement 4: changes of axial tibial rotation caused by forced rotation at the weight-bearing knee studied by RSA”, JBJS Br, 2000.

[7] martelli S, Pinskerova V, “The shapes of the tibial and femoral articular surfaces in relation to tibiofemoral movement”, JBJS Br, 2000.

[8] Pinskerova V, Iwaki H, Freeman mA, “The shapes and relative movements of the femur and tibia in the unloaded cadaveric knee: a study using MRI as an anatomical tool”, Chapter 10 in Surgery of the Knee, edited by Insall JN and Scott r, pub. by Saunders, Philadelphia, 2000.

[9] Pinskerova V, maquet P, Freeman mA, “The anatomic literature relating to the knee from 1836 to 1917: an historic note”, Clin orthop relat res, 2003.

[10] Freeman mA, Pinskerova V, “The movement of the knee studied by magnetic resonance imaging”, Clin orthop relat res, 2003.

[11] Nakagawa S, Johal P, Pinskerova V, Komatsu T, Sosna A, Williams A, Freeman mA, “The posterior cruciate ligament during flexion of the normal knee”, JBJS Br, 2004.

[12] Pinskerova V, Johal P, Nakagawa S, Sosna A, Williams A, Gedroyc W, Freeman mA, ”Does the femur roll-back with flexion?”, JBJS Br, 2004.

[13] Freeman mA, Pinskerova V, “The movement of the normal tibio-femoral joint”, J Biomecch, 2005.

[14] mcPherson A, Kärrholm J, Pinskerova V, Sosna A, martelli S, “Imaging knee position using MRI, RSA/CT and 3D digitisation”, Journal of Biomechanics, 2005.

[15] Lankester BJ, Cottam HL, Pinskerova V, eldridge JD, Freeman mA, “Variation in the anatomy of the tibial plateau: a possible factor in the development of anteromedial osteoarthritis of the knee”, JBJS Br, 2008.

[16] Pinskerova V, Samuelson Km, Stammers J, maruthainar K, Sosna A, Freeman mA, “The knee in full flexion: an anatomical study”, JBJS Br, 2009.



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mechanical stability of the AmIStem, a standardized in-vitro analysis

Abstract In vitro studies are the first steps in evaluating the behavior of an orthopedic prosthesis.The purpose of this study was to analyze the mechanical stability of the AmIStem femoral stem by medacta® International and to demonstrate that the product offers an easy introduction with AmIS® approach.The AmIStem was developed to improve the femoral component implantation during AmIS® (Anterior minimally Invasive Surgery). It is based on straight rectangular stem design and clinical experience. Specific features are a reduced shoulder and a shortened shaft.The stability test was carried out at the Heidelberg Institute where a standardized setup is used with a machine which applies an axial torque to the stem pre-implanted into a synthetic femur. measurements at different sites, on both the stem and the femur allow the evaluation of relative micro-motions, thus providing results in terms of mechanical stability.Prostheses from different manufacturers had already been tested by the same method, which made it possible to have comparative results.In conclusion, the AmIStem shows good primary stability and the typical fixation pattern of a proximal two thirds anchorage stem. The shortening is a benefit for rotational stability, whereas the fixation modus is not affected by the distal stem reduction. The reduction of the shoulder allows for easier implantation with the AmIS® approach.

mechanical stability of the AmIStem,a standardized in-vitro analysism. Bernardonia, F. Siccardib, I. Quaglianac, G. Grimoldic

IntroductionAmong approaches for Total Hip replacement

claimed to be mIS, the anterior minimally invasive approach is the only one that follows a path which is both intermuscular and internervous thus providing all the possible benefits for the patient[1].

The AmIStem femoral stem (medacta® International SA) has been developed to improve the femoral component implantation during AmIS® (Anterior minimally Invasive Surgery, medacta® Int. SA).

The AmIStem is based on the Quadra® stem (medacta® International SA) design and clinical experience[2].

Building on the advantages inherent in the Quadra® stem design, the AmIStem has been designed to offer more bone preservation and easier introduction in the femoral canal preserving effective mechanical stability. The Quadra® stem is a straight rectangular


stem successfully implanted since 2003 with more than 40’000 THA up to December 2009.

In addition, the stability of the Quadra® stem was evaluated in 2005 by a mechanical study at the Heidelberg Institute[3]. This study classified the Quadra® stem as a proximal two thirds anchorage stem that follows closely the torsion of the bone, therefore demonstrating mechanical stability and confirming the good clinical results.

In order to offer the surgeon more bone preservation and an easier implantation with mIS techniques, especially the AmIS® technique, the Quadra®-AmIS®* stem (medacta® Int. SA) was designed with a reduction of the shoulder[4]. The Quadra®-AmIS®* was introduced in 2007 in two hospitals (Uniklinik Balgrist, Dr. Claudio Dora and Dr. Fabian Kalberer; CmC Paris V, Dr. Frédéric Laude) for clinical evaluation purpose reporting no revisions[5].

Figure 1. AmIStem.

a. Medacta® International, Research & Development department, Castel San Pietro, Switzerland b. Medacta® International, Medical department, Castel San Pietro, Switzerlandc. Medacta® International, Product Management department, Castel San Pietro, Switzerland

*Not FDA cleared

33



Figure 2. From QUADrA® to AmIStem.

Following this intermediate step, the AmIStem was designed with a 15% reduction of the length to improve bone preservation and stem introduction. The mechanical test was carried out in 2008[6] and in April 2009 the first AmIStem was implanted.

This paper aims to present the AmIStem and its results in terms of mechanical stability and easy introduction.

material and methodsThe purpose of this study is to analyze the mechanical

stability of the AmIStem and to show the results in terms of easy introduction. The AmIStem prosthesis is a straight triple tapered stem made of Ti-6Al-7Nb (ISo 5832-11) and designed to have a metaphyseal fit.

The stability test has been carried out at the Heidelberg Institute, by the Laboratory of Biomechanics and Implant research where different prostheses from different manufacturers have already been tested with the same method, providing a comparison background to evaluate the results.

The tests are performed with synthetic femur (composite bone 2nd generation, #3106, Sawbone) that closely resembles the human femur in mechanical properties and dimensions. Four bones are usually used to collect data. For consistency, the stems are always implanted by the same surgeon. The bones are then assembled onto a machine that applies an axial torque to the stem and therefore to the bone (Figure 3).

Figure 3. measurements point with respect to the lesser trochanter.

This torque is time dependent ranging from -6 Nm to +6 Nm with a 0.16 Nm step. The axial torque twists and bends the bone and the stem and produces differential movements between them. moreover, a ventro-dorsal torque of maximal 3.5 Nm was applied onto the prosthesis stem to evaluate possible tilting. To track this complex behaviour it is necessary to measure the spatial motion at different sites (Figure 4). The lesser trochanter is used as the reference system. measurements are carried out at five different sites: two of them are located on the implanted stem (#1: shoulder and #2: stem apex) and the other three on the synthetic bone (#3: 8 cm below the lesser trochanter, #4: at the same level of stem apex and #5: 20 cm below the lesser trochanter).

Figure 4. measurements point with respect to the lesser trochanter.


34



The average movement for the four samples is the final outcome of the test in term of rotational stability and medio-lateral stability. For the rotational stability, a linear interpolation of the points for both stem and bone can be shown graphically and the differential movements can be compared.

resultsThe final outcome of the rotational stability test is

a graph with the Distance from the lesser trochanter as the ordinate and the Normalised angle of rotation as the abscissa (Figure 5). The broken line represents the movements of the stem while the solid line represents the bone. The identification of the points is as in Figure 4. remembering that each point in the chart comes from the average of the four samples tested, we can estimate the average relative movements between the stem and the synthetic femur.

Figure 5. rotational stability of AmIStem: the broken line represents the stem while the solid line represents the bone.

Where both lines are present, we can evaluate the behavior of the stem and the bone. At the level of the lesser trochanter, which has been taken as the reference system, the average relative motion is 5.20 mdeg/Nm whereas at the apex it is -9.97 mdeg/Nm. Following the standards of the Heidelberg protocol, these values are sufficient to guarantee rotational stability. Furthermore, the shortening is a benefit for rotational stability, whereas the fixation modus is not affected by the distal stem reduction[6].

The fixation modus is confirmed also by the imprints of the dye test: strong and constant imprints within the proximal area of the stem and little contact at the edges on the cancellous bone in the distal part of the stem. Therefore the AmIStem shows the typical pattern of a proximal two thirds anchorage and follows closely the torsion of the bone.

moreover, the tilting has been evaluated with the mean movements of stem and bone in medio-lateral direction showing good medio-lateral mechanical stability. These measurements also allow the elastic behavior of the stem to be considered. The average movements at the shoulder and at the tip of the stem are respectively 0.69 mdeg/Nm and 0.18m Deg/Nm. This can be considered as a threshold behavior with respect to other stems evaluated with the same method. Considering the fixation modus, that shows little imprints at the distal tip, and the results of the first year implantations[7], that show no tilting, we can conclude that there are no concerns also about the flexibility of the AmIStem.

As far as the introduction of the stem during AmIS® is concerned, it is very easy to measure the space required to insert the stem. It is sufficient to measure the height of the shoulder where the apex of the stem virtually touches the femoral canal following the ideal curve of insertion (Figure 6).

Using size 4 stems as reference, the AmIStem requires 41 mm while for the Quadra® stem 60 mm is required. The insertion of the AmIStem is therefore 33% easier[8]. It is important to point out that easier insertion means also less release of soft tissue, providing better results for the patient.

Figure 6. Comparison between the space required to implant the Quadra® stem (A) and the AmIStem (B).

DiscussionFollowing the experience of Quadra® stems it has

been possible to demonstrate the primary stability of the AmIStem. Both stems are suitable for every approach with promising long term results. The use of the AmIStem is particularly appropriate for the AmIS® approach due to easier insertion that allows to reduce the release of soft tissues. The shortening of the stem and the reduced shoulder in comparison with a standard straight rectangular stem design is clearly related to bone preservation, especially in the lateral part of the greater trochanter.


Distance from lesser trochanter [cm]

Normailzed angle of rotation [mdeg/Nm]

35



Clinical evaluations are planned to confirm the mechanical results. The outcomes of the first year implantations are promising[7].

ConclusionsThe AmIStem is a bone preserving implant suitable

for every approach. Features are the reduction of the shoulder and the shortening of the shaft compared to the design of a standard straight rectangular stem.

The AmIStem shows good primary stability and the typical pattern of a proximal two thirds anchorage, such as the CLS stem (Zimmer Inc)[6] and Quadra® stem. The shortening is a benefit for rotational stability, whereas the fixation modus is not affected by the distal stem reduction[6].

The reduction of the shoulder allows an easier insertion for mIS approaches and especially for the AmIS® approach.

references[1] Laude F, moreau P, Vié P, “Arthroplastie totale de hanche par voie antérieure de Hueter mini-invasive”, maitrise orthopédique 2008; (179): 6-11.

[2] moreau P, “Quadra® cementless 3 years clinical follow up”, 2008; data on file: medacta®.

[3] Heidelberg Lab-report 2005, orthopädische Universitätsklinik Heidelberg. Data on file: medacta®.


[5] Data on file: medacta®.







M E D A C T A O R T H O P A E D I CR E S E A R C H A N D ED U C AT I O N

I n s t I t u t e



medacta® orthopaedic research and education Institute, m.o.r.e. Institute, has been conceived to support healthcare professionals and improve patient outcome with:

The most effective training programmes for surgeons

Surgeon to Surgeon educational opportunities

The opportunity to share experience

more than 80 experienced surgeons worldwide are ready to support you through:

round Table Discussions

National and International reference Centre visits

Cadaver wet labs

Product Club meetings

Live Surgeries

Difficult Case evaluation

With Medacta® the surgeon is never alone.

38



39



Medacta International SA Strada regina - 6874 Castel San Pietro - SwitzerlandPhone +41 91 696 60 60 - Fax +41 91 696 60 66 - [email protected]

Headquarters

representativesSwitzerland - FrauenfeldGewerbestrasse 3 - 8500 FrauenfeldPhone +41 (0) 848 423 423 - Fax +41 (0) 848 423 424 - [email protected]

SubsidiariesAustralia - Medacta Australia PTY. LTDUnit F37, 16 mars road - Lane Cove Business Park - NSW 2066Phone +61 (2) 94202944 - Fax +61 (2) 94202578 - [email protected]

Belgique - Medacta Belgium B.V.B.A./S.P.R.L.5a rue de la maîtrise - 1400 NivellesPhone +32 67 555 482 - Fax +32 67 555 483 - [email protected]

Canada - Medacta Canada Inc.31 mcBrine Drive, Unit 11- N2r 1J1 - Kitchener, ontarioPhone +1 519 279 1934 - Fax +1 519 279 1938 - [email protected]

Deutschland - Medacta Ortho GmbHJahnstrasse 86 - D - 73037 GöppingenPhone +49 (0) 7161 5044312 - Fax +49 (0) 7161 50 44 325 - [email protected]

France - Medacta France SAS 6 rue du Commandant d’estienne d’orves - Parc des Chantereines - 92390 Villeneuve La GarennePhone +33 147 39 07 22 - Fax +33 147 39 73 17 - [email protected]

Italia - Medacta Italia SrlVia G. Stephenson, 94 - 20157 milanoPhone +39 02 390 181 - Fax +39 02 390 00 704 - [email protected]

Japan - Medacta Japan CO. LTD100-0014 Chiyoda House 201 - 2 - 17-8, Nagatacho, Chiyoda-ku, TokyoPhone +81 (0) 3 5510 8883 - Fax +81 (0) 3 5510 8884 - [email protected]

Portugal - Medacta Portugal SArua João de Deus 4 B - 2665-235 malveiraPhone +351 21966 7590 - Fax +351 21 966 7591 - [email protected]

UK - Medacta UK Limited9 Cartwright Court - Cartwright Way - Forest Business Park Bardon Hill - Leicestershire - Le67 1UePhone +44 (0) 1530 830451 - Fax +44 (0) 1530 839326 - [email protected]

USA - Medacta USA4725 Calle Quetzal Suite B - Camarillo - California 93012Phone +1 805 437 7085 - Fax +1 805 437 7089 - [email protected]

Argentina

DistributorsAustria Brazil Greece South Africa Spain The NetherlandsIndonesia

M.O.R.e. JournalRef: 99.99.journal02Rev. 00

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[1] Baldo F, Boniforti B - Patient-specific cutting blocks for total knee arthroplasty: preoperative planning reliability. J Orthopaed Traumatol (2011) 12 (Suppl 1): S23-S88. [2] Koch P et al - Guide de coupe sur mesure pour PTG: présentation de la technique opératoire et résultats radiologiques préliminaires. Podium Presentation at the 86th Annual Congress of the SOFCOT, Paris, France, November 7-11, 2011. [3] Koch P - MyKnee® System: a new vision in total knee replacement. Leading Opinions - Orthopädie & Rheumatologie 2, 2011: 32-35. [4] Leon V - Patient matched technology vs conventional instrumentation and CAS. Podium Presentation at the 6th M.O.R.E. International symposium, Stresa, Italy, May 13-14, 2011. [5] Müller et al - CT based patient-specific cutting blocks for total knee arthroplasty: technique and preliminary radiological results. Podium Presentation at the 71st Annual Congress of the SSOT, Lausanne, Switzerland, June 22-24, 2011. [6] Goldberg TD - MyKnee® economical and clinical results. Podium Presentation at the 6th M.O.R.E. International symposium, Stresa, Italy, May 13-14, 2011.

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